We conducted an ornithological survey of the Colombian slope of Cerro Tacarcuna, the highland region adjacent to the ‘Darién Gap’ on the Colombia / Panama border, and one of the most poorly known and threatened regions in the world. We present novel data on distribution, habitat, breeding biology and vocalisations for 27 species, including the first confirmed records in Colombia of Ochraceous Wren Troglodytes ochraceus and Beautiful Treerunner Margarornis bellulus, and the first records in the Darién highlands of Black-headed Antthrush Formicarius nigricapillus, Scaly-throated Foliage-gleaner Anabacerthia variegaticeps, Yellow-throated Chlorospingus Chloropingus flavigularis hypophaeus and, based on previously overlooked specimens, report the first confirmed records for Colombia of Sooty-faced Finch Arremon crassirostris. In addition, we collected the first Colombian specimens of Violet-capped Hummingbird Goldmania violiceps, Bareshanked Screech Owl Megascops clarkii, Tacarcuna Tapaculo Scytalopus panamensis and Varied Solitaire Myadestes coloratus. For several subspecies endemic to the region, we collected the first or second specimens for Colombia. Finally, we discuss the elevational ranges of Darién endemic species and subspecies, which are mostly concentrated above 600 m. The Darién highlands remain poorly studied and threats to their conservation are increasing. Therefore, effective measures are needed, particularly in Colombia, where the sole protected area in the region currently covers forests only below 600 m.